1. Technical Field
The present invention relates to the conversion of liquid fuel to gaseous form and particularly to a method and apparatus for producing a flow of combustible gaseous mixture of fuel and air for use in a combustion apparatus, particularly in an internal combustion engine.
2. Background Art
Recent efforts to reduce fuel consumption and pollution of internal combustion engines have been directed increasingly to the problems of nonuniform mixing of fuel and air and of fuel condensation in the intake passages. In conventional venturi carburetors, liquid fuel is delivered in a finely-divided spray, part of which tends to condense upon cold intake passage walls. To assure that a combustible mixture will reach the cylinders, the carburetor must be adjusted to give a rich mixture during engine warm up. In addition, the delivery of fuel in the form of directional droplets makes it difficult to achieve completely uniform mixing with the intake air flowing through the carburetor.
Attempts to solve this problem have focused on methods and apparatus for heating the fuel/air mixture and/or heating intake passage surfaces, either electrically or by exhaust gases, to promote vaporization of the fuel. The mixture heating may be accomplished in conjunction with rotational mixing, as in U.S. Pat. No. 4,053,013 of P. Guba, U.S. Pat. No. 4,264,539 of R. E. Borg, and U.S. Pat. No. 4,311,128 of G. Bernecker.
Bernecker also teaches passing a spray of liquid fuel mixed with air through a porous medium to improve atomization, as does L. L. Wallace in U.S. Pat. No. 3,711,257. U.S. Pat. No. 4,150,954 of J. Abthoff et al. discloses the use of a catalyst on a porous support for splitting a mixture of air and diesel fuel into combustible gaseous components, such as H.sub.2, CO, and CH.sub.4, and also containing CO.sub.2 and H.sub.2 O. The catalytic reaction requires a relatively high temperature, induced initially by glow plugs and maintained either by premixing pure air with the fuel to create an exothermic reaction or by premixing hot exhaust gases with the fuel to create an endothermic reaction.
An obvious drawback to heat augmented fuel vaporization or splitting is the increased risk of fire, particularly when the fuel is mixed with air to form a combustible mixture prior to or concurrently with the heating. In addition, when the combustion air is combined with the liquid fuel before passing the mixture through a porous medium to fully evaporate the fuel, a very large flow cross section is required to avoid unacceptably high pressure drop through the porous medium.